The present invention relates to thermoplastic composites and methods of making the same, and more particularly to a composite formed by a novel method that can be carried out at ambient temperature.
Conventional methods of making thermoplastic composites are expensive and limited compared to those for making thermoset composites. The key reason for such a distinction is the relatively high viscosities associated with thermoplastics which makes it difficult to obtain the necessary wetting of the filler to produce a uniform, cohesive end product.
However, various applications for composites make it desirable and necessary to utilize thermoplastic composites as opposed to thermoset composites. One reason is that thermoplastic composites are desirable because thermoplastics are generally less expensive than thermoset polymers. In addition, the desired properties of a composite may require using thermoplastic polymers instead of thermoset polymers.
Presently, there are at least two known methods of mixing thermoplastic polymers with powdered fillers. In one method, solid thermoplastic pellets and powdered filler are pre-mixed and then passed through a heated extruder where the pellets are melted, the pellets and filler are mixed by mechanical means and ejected from the extruder. In another application, heat and extremely high pressure are used to force the mixture of thermoplastic pellets and powdered filler through a die and into a mold.
To mix thermoplastic polymers with non-powdered fillers, there are at least three conventional methods. In one method, filler particles are individually dipped in a hot viscous bath of thermoplastic, and then after cooling, the dip-coated filler particles are woven into a fabric-like form. Next, such fabric-like material is positioned in a mold with additional thermoplastic material. Heat is then applied causing the thermoplastic to melt into and around areas of the fabric-like material to fill in dry spots where the dip-coating step may not have sufficiently worked.
An alternative method is to use extremely high pressure injection of thermoplastic material into a mold to coat certain types of fillers. Only certain types of fillers are usable for such an application.
In addition, it is known to make relatively thin sections of composite material by layering thermoplastic pellets and filler material in a mold followed by heating the mold.
It is therefore an object of the present invention to provide a blend for forming a thermoplastic composite that does not require using conventional, expensive techniques for achieving proper wetting between the thermoplastic and filler material.
Another object of the invention is to provide a method of making a thermoplastic composite that does not require a heating/mixing step after forming a blend of thermoplastic pieces and filler particles.
A still further object of the present invention is to provide a thermoplastic composite that is a solid, homogenous, non-foamed material that can be easily and relatively inexpensively produced.
Yet another object of the present invention is to provide apparatus for making a reinforced thermoplastic composite from the blend of thermoplastic pieces and filler particles.